Tuned circuit



P. GANTET TUNED CIRCUIT July 8, 1941.

Filed Jan. 18, 1939 ffm Patented July 8, 1941 Application January 18,1939, Serial No.1251`,(u1-5 In France January 27, 1938 6` Claims.(01.178244) The present invention relates to apparatus for varying theelectrical characteristics of oscillating circuits.

The contact resistances encountered by high frequency currents whenpassing from the stationary part to the movable part lof an adjustableoscillating circuit andmore exactly the variations of these resistancesduring the adjustment (or under the effect of vibrations) are the sourceof very troublesome disturbances.

In a receiver such resistances modulate the amplitude of the signalreceived or of thelocal oscillation and are translated by violentgrinders, which render listening-in or signal finding very laborious.

In a Wave-trap theypartly mask the exact tuning, and thus limit theaccuracy of the measure. Y

These deficiencies are vparticularly marked in the range of very shortWaves.

In the French Patent No. 821,290 dated August '7, 1936, an adjustableoscillating circuit for very short Waves has been described,characterised by the absence of any contact resistance in the path ofthe oscillating current. The total range was passed over during arotation of 186 of the movable part.

The present invention relates to another embodiment of lan adjustableoscillating circuit for metric or decimetric waves having no variablecontact resistances in the path of the oscillating current and capableof covering a Wider range. This range is passed over by a longitudinaldisplacement of the movable part. v

This oscillating circuit comprises two con ducting parts or electrodesinsulated from each other which have the shape of rotatable coaxialbodies one of which is axially movable relatively to the other, in orderto vary the Width of the annular space separating them. The outerelectrode is usually stationary and the inner electrode movable, but areverse arrangement may be adopted.

These electrodes preferably comprise concentric frustum shaped surfaceshaving one and the same angle of conicity.

The outer electrode is preferably closed at both its ends so as tocompletely surround the inner electrode.

The latter is usually composed of .two co-axial parts spaced apart andrigidly connected by a stay member of reduced diameter, one of theseparts being irustum-shaped and the other being either frustum-shapedWith a similar or dilTerent conicity, or cylindrical. The outerelectrode has a corresponding shape with theexceptionthat vit does :notcomprise a reduced .part capable of hinderingthe axial Ydisplacement of.the inner electrode. y. i. The annexed dravvingillustrateadiagrammatically and by Way of examples only,r several forms ofconstruction of. Vthe subjectfmatterof thel invention, seen in axialsection. Y

Figs. 1,- 1'a,: 2*, y3 vand 4' areV axial sections Yof five differentembodiments. 1

`lilig.5' s'hovvsk inv axial. sectionjjthe upper part of .=anotl1'er,embodiment asf-Well: as the. diagram of an; oscillating; circuit,.coupled :with thelsub- .ject-matter-of theinyentioin Figs. 6, 7 andn 8arediagrams of three other -modications inpwliichthe rcontrol' meanshave `not been shovvnzl` n i The arrangement shown-in vlifig. 1includesan inner movable insulated electrodeor conducting part formed bytir/to frustum-shaped caps I and 3" ofrelatively large averageVdiameter, connected ybya cylindrical rod or tube 2 of an appreciablysmaller .diameteln A stationary outer electrode orconducting vpart 4lis-"provided, .inthe shape of a; hollow truncated cone closed at bothits ends, which completely surrounds the 'movable part and thexaxis ofwhichis.common'to'theparts land 3. y L

The movable part isgcentered inthe stationary vpart and insulated from;the latter by Itvvo insulators 5; and-6 secured kto the metallicmembersjl'andgrigid Withthe caps l and 3. AThe other endsfjof theinsulators are attached to cylindrical rods 9` and l0 slidillgginbearings Il and I2 secured on; the cheek membersv` oi the stationarypart. These two, insulators and 6 Carr be combined in al single; memberSCL-passing .throughtne tube 2, as indicated innig. 1a.

Thegself-inductancey of .the,oscillating circuit thus formed is mainlyconstituted by the tube or rod'Zzf The capacity;` c f the circuit isthat of .the two condensers which are respectively constituted bythecaps ljand 3 and the common casing 4 which connects them in series.. l

It is to be notedthat the elementsv ofthis c ir cuit present electriccharacteristics of self-in- .ductance and capacity which are notstrictlyuniform; Furthermore, this distribution lchanges withthe'adjustment; as, Well as the distribution ofthe voltages between'thetwo condensers. 'Ihe whole nevertheless remains easily computable. Adisplacement of the movable part along its axisin the directionofthe-arrow provides a .very slight 'reduction` of the self-inductanceand anappre'ciable"increase of the tuning capacity 'I'he circuit isadjusted by rotating an external hand wheel keyed on 9 or I0.

For certain applications, the appreciable increase of the capacity of anelement of the conF denser, or the modification of its law of variationrelatively to that of the other element, preshaped cap I will be givenan angle at 'the apex l different from that of the cap 3 and the shapeof the casing 4 will be correspondingly modified, as shown in Fig. 2.For the same purposes, the arrangement described above with reference toFig. 3 can also be adopted according to the invention.

The movable insulated conducting part is constituted by a frustum-shapedcap I and a cylindrical cap 3 connected by a cylindrical rod or tube 2.

The stationary metallic part 4 is of frustumshape on that portion of itslength which is opposite the frustum-shaped cap I. 'Ihe part 4 iscylindrical opposite the cylindrical cap 3. Ap-

proximately the same diameters can be given to the cylindrical parts 3and 4 and thus the capacity between them can be increased withoutappreciably increasing the length.

With this arrangement, the insulation can remain such as provided anddescribed with reference to Fig. 1. If the high frequency voltagebetween the p-arts 3 and 4 is much lower than the voltage between I and4, use can be made on the side 3 of a more rugged insulator. As

illustrated in Fig. 3 the movable part can be L mounted in anoverhanging position.

The movable part can also be insulated as illustrated in Fig. i'whereinthe insulators comprise insulating washers 5 and 6 secured at threepoints at 120 on bosses 'I' and 8 mounted on the movable part, and atthree other points offset to the extent of 60 relatively to thepreceding ones on metallic star-shaped members having three branchesrigid With a metal shaft passing Within the tube 2. The metallic circuitconstituted by the shaft and the casing being iirmly coupled to theoscillating circuit must be interrupted, either by cutting the shaft asillustrated Fig. 4, or by insulating one of its lends by means of aninsulator I3, as shown in Fig. 5. In this case, according to theinvention, the metal shaft can be used as coupling member for couplingthe oscillating circuit with an outer circuit I4, I5 connected to theinsulated 'en dfof said shaft and to the casing. "These oscillatingcurrents spread on a very small thickness of the outer surface of themov- 'able part and of the inner surface of the stationary part.Consequently, any desirable shape can be given to the outside of thestationary part and tothe inside of the movable part, and use 'can bemade for their construction of materials which are only slightlyconducting covered with alayer of good conducting material. The rel-'ative' proportions different from'those illustrated can be chosen andthe axial length can be given any dimension considered suitablerelatively to the wave length.

I claim:

1. Apparatus for varying the electrical characteristics of anoscillating circuit comprising, an electrode lproviding a casing andhaving a conical portion, an electrode arranged coaxally within thecasing, said inner electrode including two electrically conductivemembers spaced from said casing to provide capacitative couplingsvbetween the casing and each electrically conduc tive member, one ofsaid members having a conical portion arranged adjacent the conicalportion of the casing, means electrically connecting said members, meansinsulating Said inner electrode with respect to the casing andsupporting the inner electrode for axial movement with respect to theother electrode.

2. Apparatus for varying the electrical characteristics of anoscillating circuit comprising, a conical shaped electrically conductivecasing, two eletcrically conductive members arranged Within said casing,said members having conical shaped peripheral portions spaced from saidcasing to provide capacitative couplings between the casing and theperipheral portion of each of said members, axially arranged means ofsmaller diameter than said members electrically connecting the members,means supporting said members for axial movement with respect to saidcasing, and means insulating said members with repect to said supportingmeans.

3. Apparatus for varying the electrical characteristics of anoscillating circuit comprising, a conical shaped electrically conductivecasing, two electrically conductive members arranged within said casing,said members having conical shaped peripheral portions spaced from saidcasing to provide capacitative couplings between the casing and theperipheral portion of each of said members, axially arranged means ofsmaller diameter than said members electrically connecting the members,means supporting said members for axial movement with respect to thecasing and insulating said members with respect to the casing.

4. Apparatus for varying the electrical characteristics of anoscillating circuit comprising, a conical shaped electrically conductivecasing, two electrically conductive members arranged within said casing,said members having conical shaped peripheral portions spaced from saidcasing to provide capacitative couplings between the casing and theperipheral portion of each of said members, axially arranged means ofsmaller diameter than said members electrically connecting the members,means supporting said members for axial movement with respect to saidcasing, means insulating said members with respect to said supportingmeans, and means for moving said members axially with respect to thecasing.

5. Apparatus'for varying the electrical characteristics of anoscillating circuit comprising, an electrically conductive casing havinga cylindrical portion and a conical portion, two electrically conductivemembers arranged within said casing, one of said members having aconical shaped peripheral portion spaced from the conical portion ofsaid casing to provide a capacitative coupling between the conicalportion of the casing and the conical shaped periphery of `said member,the other member having a cylindrical shaped peripheral portion spacedfrom. the cylindrical portion of the casing to provide a capacitativecoupling between the cylindrical portion of the casing and thecylindrical peripheral portion of said member, axially arranged means ofsmaller diameter than said' members electrically connecting the members,and means supporting said members for axial movement with respect to thecasing and insulatiing said members with respect to the casing.

6. Apparatus for varying the electrical characteristics of anoscillating circuit comprising, a conical shaped metal casing, two metalmem-

